The conventional self-tapping screws are commonly used for fastening the metal corrugated boards to the roof of a structure or to a metal girder of the side walls of the structure. The tooth pitch and the tooth depth of the conventional self-tapping screws are kept relatively small so as to avert the damage or destruction of the advancing spiral ridge of the conical shank of the conventional self-tapping screw at the time when the conventional self-tapping screws is fastened onto a metal girder.
In order to prevent the room temperature from rising excessively, the metal corrugated boards and the horizontal metal girders of the structure are provided therebetween with an insulating layer of the polyurethane (PU) foam material or glass fiber cotton material. The conventional self-tapping screws do not engage well with the insulating layer described above.